Embodiments of the present invention relate to an image capturing unit comprising a lens and image sensor, and their methods of manufacture.
An image capturing unit 20 comprises a lens module 24 which directs an image onto an image sensor 28, as for example shown in FIG. 1. The lens module 24 comprises a lens 30 mounted in a lens barrel 32. The image sensor 28 can be a CCD or CMOS array 36 having an image receiving surface 38 that converts an incident image, which may be light, infrared or other radiation, into an electronic signal. Typically, the image sensor 28 is enclosed in a package 40 that is fabricated by chip on board (COB), tape carrier package (TCP), chip on glass (COG) methods, or Chip Scale Packaging (CSP) either with lateral connections or Through Silicon Via (TSV). A lens holder 42 joins and aligns the lens module 24 to the image sensor 28 in the package 40. The image capturing unit 20 is used, for example, in electronic devices such as mobile phones, personal digital assistants, remote sensors, signal transmitting cameras; medical devices; and applications such as a lens for a car security system.
It is difficult to cost effectively fabricate image capturing units 20 with ever smaller sizes as it becomes increasingly difficult to properly position or align the small lenses 30 relative to the image sensors 28. For example, each lens 30 has to be at a particular height above an image sensor 28 that reflects the focal length of the lens 30. During testing of an assembled unit, the height of lens 30 can be set by adjusting the height of the lens barrel 32 inside the lens holder 42 by turning it, either by automatic or manual means. However, this step requires the thread 33 to have a high degree of accuracy which provides incremental height adjustments that can be as small as 1 micron, without causing loss of centering of the lens 30 or tilting. Also, the height adjustment step adds time and labor costs to the alignment and assembly process.
It is also often difficult to align the axis of a lens 30 to be parallel to the central axis of a lens barrel 32 during assembly of the lens module 24. Alignment of these two axes renders the axis of the lens and barrel perpendicular to the image receiving surface 38 of the image sensor 28. However, even a slight degree of misalignment will cause the image generated by a lens 30 to become unfocused. Further, during assembly of each image capturing unit 20, each lens module 24 is manually positioned and attached to an image sensor 28, and alignment issues can also arise in this positioning step.
In addition, the unit assembly, lens alignment and height positioning steps should be accomplished while retaining structural integrity of the lens module 24 and image sensor 28. It is also desirable to have a reliable assembly process which provides good alignment of the lens modules 24 to the image sensors 28 and proper height of the lens 30, and does this in a cost effective manner.